Difficult for me to say, we don'ty know anything about your functions, but your first function expects a pointer to the int values. Passing a reference to your variables seems to be the right way to do so (and that's what I am doing quite regularly when calling relatively similar libraries). As for the second function, it expects values, so you would need to pass directly your variables.

I am a but surprised, though, that your C functions don't return any values (not even an error code).